Method of making a heat exchanger tube



3, 1960 T. F. PAULS 2,949,664

METHOD OF MAKING A HEAT EXCHANGER TUBE Filed Jan. 1a, 1956 2 Sheets-Sheet l Aug 23, 1960 1-. F. PAULS METHOD OF MAKING A HEAT EXCHANGER TUBE 2 Sheet s-Sheet 2 Filed Jan. 13, 1956 22 ww m a y w 2 .7 NW

METHOD OF MAKING A HEAT EXCHANGER TUBE Theron F. Pauls, Godfrey, 111., assignor to Olin Mathieson Chemical Corporation, East Alton, 111., a corporation of Virginia Filed Jan. 13, 1956, Ser. No. 559,060

9 Claims. (Cl. 29-1573) This invention relates to the art of manufacturing heat exchangers and more particularly to the manufacture of a loop or zigzag type of heat exchanger conduit having one or more return bends.

Tubes for heat exchanger devices such as heating or cooling coils are frequently constructed by providing a long length of conduit or tubing which is then bent one or more times at a relatively sharp angle over 180 to obtain a required and relatively large number of coils passing back and forth in a given limited area or heat exchanger space. In many installations, it is desirable that the heat exchanger be constructed of sheet metal. Furthermore, it would be desirable to shape the entire tube of one or more loops by application of inflation fluid internally, but the bending of such tubing presents considerable difliculty since this type of tubing tends to form a restriction even more readily than round, relatively thick walled tubing. It is necessary that there be provided a bend without restriction of the tube passageway, in order that flat, relatively thin walled tubing. can be laid up to form a fairly dense heat exchanger core having a plurality of loops of the tubing with free flow of fluid from end to end.

One object of this invention is to provide a heat exchanger core made up of two or more relatively flat tubular heat transfer elements of the type produced from sheet metal. Another object is to provide a heat exchanger unit formed from a number of loops of an elongated tubular member deformed at intervals so as to enable the tubular member to be bent in a zigzag manner into a sinuous form without constricting the tube excessively at the bend. Another object is to provide a tubular conduit with a return bend and with substantially no restriction of the tube passageway at the bend. Still another object is to provide a new and improved method of tube shaping characterized by simplicity and economy for manufacturing a loop type of heat exchanger. A still further object is to provide a method of manufacture adaptable for mass production of such heat exchangers.

Other objects and advantages will become apparent from the following description of various specific embodiments when taken in connection with the accompanying drawing in which:

Fig, 1 is a fragmentary perspective view partly in cross section at a cut-away portion of a tube bend structure in accordance with one embodiment;

Fig. 2 is a perspective view of fragments of a length of sheet metal blank in one stage used in making the tubular element of Figure 1 and also showing the working ends of apparatus used in this stage;

Fig. 3 is a fragmentary side view of the collapsed blank of Figure 2 in another stage of manufacture in suitable apparatus;

Fig. 4 is a fragmentary semi-diagrammatic sectional view showing the blank and apparatus of Figure 3 in a further stage of operation with part of the blank shown after development by inflation;

Fig. Sis a partial cross sectional, fragmentary view of a r in modification of the blank and apparatus in the stage corresponding to that shown in Figure 2;

Fig. 6 is a cross sectional view of the completed return bend after inflation to provide another embodiment of the tube structure made from the blank of Figure 5;

Fig. 7 is a fragmentary view of a portion of another form of tube blank and the Working ends of apparatus in the stage of manufacture corresponding to that shown in Figure 2;

Fig. 8 is a cross sectional View at the completed return bend of the finished tube made with the blank of the type shown in Figure 7 and providing still another embodiment;

Fig. 9 is a fragmentary cross sectional view of one bend structure at an intermediate stage between those shown in Figures 5 and 6; and

Fig. 10 is a fragmentary cross sectional view of another bend structure at an intermediate stage between those shown in Figures 7 and 8.

In accordance with this invention, there is provided a loop or zigzag folded type of conduit or serpentine tubing relatively free from restriction at the bend. It is also contemplated that the manufacture of such tubing by fluid filling and fluid forcing be made possible by a special construction at the bends or fold so as to permit continued and unhindered passage of the fluid throughout the length of the internal passageway of the tubing. This is accomplished by providing a preliminary bend in a special tube blank consisting of a flat, collapsed tube or of superposed component strips joined at their lateral edges but otherwise parted to enable inflation. The preliminary bend is made in a direction opposite to that which will be taken by the return bend of the finished tubing. When such a preliminary bend is first provided and then afterward the primary or main bend is made, this preliminary bend forms an inside bulge which influences the resultant distention desirably during the inflation operation. The preliminary bend is generally of smaller radius or of sharper configuration than the primary bend. The preliminary bend may actually consist of a number of bends embraced by the primary bend which is formed afterward.

The purpose of the preliminary bend is to form on the inside of the main bend one or more bulges to affect and thereby control the shape of the distention of the tube walls at the bend, and especially the distention occurring on the inside of the bend. The preliminary bend in one direction, together with the reverse second or main bend, provides an intermediate structure characterized by one or more bulges in desired places on the inside of the return bend of the collapsed tube strip or blank. When internal pressure of suflicient magnitude to accomplish inflation is injected into this blank, the finished tube loop or serpentine structure, including a return bend with free flow, results. Thus, the preliminary bend predisposes the distention in a desirable Way at the bend.

In the embodiment illustrated in Figure l, the unit includes an incoming tube sheet 1 and an outgoing tube sheet 2 both of which are interconnected by the return bend 3 to form a conduit loop. Sheet 1 contains incoming passageways 4, while sheet 2 is provided with outgoing passageways 5, which like passageways 4 have been developed by distention under internal fluid pressure. Each passageway 5 is interconnected with a corresponding passageway 4 by means of a fold of the type shown. The return bend portion or interconnecting passageway 6 between portions 4 and 5 is simultaneously developed likewise by distention under internal fluid pressure. When completed, this portion of the tube consists of an outside curved wall 7 and an inside wall 8 at the bend including two reverse inwardly extending loops 9 and 10. This tube structure at the bend allows free circulation of heat exchanger fluid from passageways 4 through the return bend 6 to passageway 5.

The structural features shown in Figure l are all developed by distention in accordance with this invention beginning with a flat collapsed but laminated special tube stock which is given a first or preliminary bend as shown in Figure 2 and is then given a second or main bend as shown in Figure 4 to form a looped or zigzagged conduit or heat exchanger unit.

A suitable length of tube strip 10 Figure 2), having laminations in a stratum of separation 17 adapted for taking internal fluid pressure and for the ultimate generation of tube passageway in strip 10, is provided with a first or preliminary set of bends 11 and 12. These bends 11 and 12 alternately extend in opposite directions as shown. Each of the bends 11 may be formed in any suitable bending device such as between the die 15 and its mate 16. Likewise, the bends 12 are formed in the reverse direction between bending dies 13 and 14.

A strip 10 thus provided with a series of alternate bends 11 and 12 is next disposed in suitable apparatus for zigzag folding the strip 10.

One such suitable apparatus is shown in Figure 3 with tube stock 10 disposed therein with suitable orientation with respect to the preliminary bends 11 and 12. The apparatus consists of a first set of mandrels 21 disposed on one side of the tube blank or stock 10 and a second set of mandrels 22 disposed on the other side of the stock. Mandrels 21 have a suitably concaved leading end 23 about which strip 10 is folded reversely at preliminary bends 11 to form one series of loops without obliterating the bends 11. Mandrels 22 are similarly provided with a leading end 24 about which the strip 10 is reversely folded at the preliminary bends 12 to form the intermediate series of loops which, together with the first series, form a zigzag structure. In operation, each of the mandrels of the group 21 are moved between adjacent mandrels of the group 22 so that the mandrels 21 and 22 pass each other in parallel relationship. At the same time, the lateral spacing between mandrels is decreased. This may be accomplished by any suitable mechanism such as the lazy-tongs levers 25 and 26 having two series of inter-connections one series of which such as 27 and 28 are fixed on the mandrels 21 and 22, respectively, for pivotal movement while the other series of interconnections such as 29 and 30 operate in slots 31 and 32 of mandrels 21 and 22, respectively. Although Figure 3 is only a fragmentary view, it will be understood that the foresections of mandrels 21 and 22 are long enough to make the desired length of the loops and that the rearward parts of mandrels 21 and 22 are likewise of suflicient length to permit the sliding pivots 29 and 30, respectively, to move back for a suflicient distance to permit strip 10 to be folded up in accordance with one example of this invention.

When the mandrels of the apparatus shown in Figure 3 are completely closed up and the stock 10 folded up to form a serpentine heat exchange element, the parts are as shown in Figure 4 with mandrels 21 interfitting between the mandrels 22 in relatively closely spaced parallel relationship. As a result of the bending and folding operation, each of the preliminary bends 11 becomes a preliminary inside bulge 51 at the end 53 of one set of loops; and likewise preliminary bends 12 become preliminary bulges 52 on the inside of the end of the loop 54 of the intermediate loops.

The mandrels 21 and 22 are then backed up somewhat so as to increase their spacing from each other a bit and so as to also withdraw the mandrel ends 23 and 24 to increase their spacing at the mandrel ends from the preliminary bulges 51 and 52, respectively. In this condition, inflation pressure may be admitted at one or both ends of the laminated blank 10 to develop the internal passageways of the resultant tubing. While the folded tube blank may conveniently be inflated as well as folded back and forth between suitably spaced mandrels of the bending apparatus as shown in Figure 4, it will be understood that the inflation may occur in any other suitable fixture or die which would consist essentially of spaced mandrels between a pair of outside back-up members.

As shown on the right side of Figure 4, the inflated finished tubing consists of a pair of straight parallel spaced legs 61 and 62 interconnected at the return bend 66. Each return bend 66 corresponds to the structure shown in Figure l and consists of an outside distended wall 67, an inside distended wall 68 and the two inwardly extending reverse loops 69 and '70.

The preliminary bend is subject to modification. For example, instead of the sharp bend shown in Figure 2, the preliminary bend of tube blank or strip 10 may be a bend of greater radius providing a more gradual bend 81 (Figure 5 The strip is given this bend in any suitable bending dies such as 84 and 85, which are correspondingly formed with rounded instead of V-shaped working faces as shown in Figure 5.

When a blank of this type having preliminary bend 81 is inflated, the return bend 86 of the completed loop of the tubing has the appearance shown in Figure 6 where the inside distended wall 88 has greater extension in the direction of the tube passageway. Correspondingly the inwardly extending reverse loops or folds 89 and 90 are less pronounced and, consequently, this modification provides a type of loop which is preferred. In fact, in this embodiment the inwardly extending loops 89 and 90 might be considered continuations of the incoming and outgoing passageways 81 and 82, respectively, intervened only by the divergent portion at the loop formed by the inwardly distended wall 88.

In the embodiment shown in Figure 7, the blank is provided with a preliminary bend 91 of more complex form which in this embodiment includes two adjacent component bends 92 and 93, spaced to suit the final spacing between the parallel legs of the loop to be formed which carry the incoming and outgoing passageway or passageways, as the case may be. The preliminary bend 91 is shown between the working ends 95 and 94 of the bending dies or hammer suitable for the purpose.

When the blank 10, with one or more preliminary bends 91, is subsequently reversely bent over a folding mandrel to form a tube loop and then subjected to internal inflating pressure, the return bend 96 of the fin ished tubing takes the form shown in Figure 8. Here the inwardly distended wall is made up of two portions, 98a and 98b, and instead of two reentrant folds there is only one, 99. It will be appreciated that this embodiment likewise provides little or no restriction or interference with the continuity of fluid flow between the incoming passageway 101 and the outgoing passageway 102.

The intermediate form of the preliminary bend, while illustrated in Figure 4 at the inside bulges 51 and 52, will be better understood with reference to Figures 9 and 10. In Figure 9 a return bend 106 is shown in cross section through a laminated portion of the tube strip or blank. The outside wall 107 of the blank takes the usual curvature, but the inside wall 108 forms a bulge 151 protruding on the inside of the bend. This cross section is typical of the intermediate stage produced with the preliminary bends of Figure 2 and Figure 5. With a preliminary bend of the type shown in Figure 7, the intermediate structure produced is that shown in Figure 10 where the return bend 206 consists of the outside wall 207 and the inside wall 208 separated at the lamination. The preliminary bends 92 and 93 of the tube blank form the bulges 252 and 253 respectively, protruding on the inside of the bend as shown in cross section. These bulges influence the erection of the tube walls by fluid pressure inflation so as to control the distention of the inside walls. Thus, the intermediate structure of Figure 9 always results in the final or finished bend structure of Figure 6; and the intermediate structure of Figure 10 always results in a finished tube bend of the kind shown in Figure 8.

By means of this invention, there is provided not only a loop or zigzag type of tubing with relatively unrestricted fluid flow or passageway at the bend but also a method of making the tubing by bulging with a fluid medium under pressure without interruption or limitation on account of constrictions at the bend. This gives in tubing of relatively heavy as well as thin gauge walls, a return bend with a passageway cross section equal or greater than the cross section of the passageway in the adjoining straight or leg portions of the loop structure of tubing.

Although the foregoing is a description of what is now believed to be a preferred embodiment, it will be understood that those skilled in the art may make further changes and modifications therein without departing from the spirit and scope of the present invention as set forth in the appended claims.

What is claimed is:

1. The method of making a folded tube structure from a flat longitudinally laminated sheet metal blank having a first component strip superposed upon a second strip the lateral edges of which are integral with the lateral edges of said first strip and the intervening portion of which includes at least one longitudinally extending area of separation between the opposing walls of said strips defining a corresponding longitudinally extending embryonic passageway, which comprises the steps of deforming a portion of said blank intermediate the longitudinal ends thereof and transverse said embryonic passageway into a V-shaped first bend transverse said embryonic passageway, bending said blank at the said portion in a direction reverse to said first bend into a second bend also transverse said embryonic passageway and including said first bend whereby the inner wall of said separation at said second bend is deformed into a W-shaped bulge, said bending disposing the portion of said blank adjacent said second bend into parallelism to form a tube blank loop, and subjecting said bent tube blank to internal fluid pressure along said area of separation to open a longitudinal tubular passageway portion of the folded tube blank and simultaneously distend a wall portion of the tubular passageway on the inside of the second bend for uninterrupted passage of fluid throughout the length of the resultant folded blank.

2. The method of making a folded tube structure from a flat sheet metal blank having at least one longitudinally and internally extending stratum of separation defining a corresponding longitudinally extending embryonic passageway laterally contained and defined Within solid unseparated portions of said blank which comprises the steps of bending said blank along a portion of said blank intermediate the longitudinal ends thereof and transverse said embryonic passageway into a first bend transverse said embryonic passageway, bending said blank 180 into a second bend along said portion in a reverse direc tion with respect to said first bend and including said first bend to dispose the ends of said blank adjacent said second bend into substantial spaced parallelism to form a tube blank loop whereby the inner portion of said blank opposite said separation at said second bend is bulged away from the outer portion of said blank opposite said separation at said second bend, and then subjecting said bent tube blank along said stratum to internal fluid pressure sufliciently to open a longitudinal tubular passageway portion and simultaneously distend said bulge to prevent constriction of said tubular passage way portion at said second bend.

3. A method of making a folded tube structure from a flat sheet metal blank having at least one longitudinally and internally extending stratum of separation defining a corresponding longitudinally extending embryonic passageway laterally contained and defined within solid unseparated portions of said blank which comprises the steps of deforming on at least one line transverse said embryonic passageway a portion of said blank intermediate the longitudinal ends thereof and transverse said embryonic passageway into a first bend transverse said embryonic passageway, bending said blank into a second bend of greater radius than said first bend at said portion in a reverse direction with respect to said first bend whereby the inner portion of said blank opposite said separation at said second bend is bulged away from the outer portion of said blank opposite said separation at said second bend, and then subjecting said bent tube blank along said stratum to internal fluid pressure suflicient to open a longitudinally extending tubular passageway while limiting the distention of portions of said blank adjacent said second bend between rigid spaced surfaces.

4. The method of claim 3 wherein the first bend is of relatively large radius but less than the radius of said second bend.

5. The method of claim 3 wherein said first bend is formed by deforming said portion along two spaced lines transverse said embryonic passageways.

6. The method of making a folded heat exchanger tube structure which comp-rises providing a longitudinally extending tube blank having a pair of opposed walls and a longitudinally extending area of separation between said Walls defining a corresponding longitudinally extending embryonic passageway laterally contained and defined within integrally secured portions of said Walls, preliminairily bending said blank at least once at longitudinally spaced portions thereon to form first bends transversely of said passageway, then bending said blank at said portions in a reverse direction with respect to said first bends to form second bends of greater radius than their corresponding first bends, and then expanding said blank with suflicient internal fluid pressure applied along said area to said opposed walls of said blank spaced thereat including the wall portion at the preliminary bend on the inside of each second bend to form a tubular passageway unconstricted at said second bends.

7. The method of claim 6 wherein the final bending occurs around the ends of spaced parallel mandrels and wherein inflation occurs to form a serpentine tube while the bent blank is folded back and forth to pass between adjacent ones of said mandrels.

8. The method of making a heat exchanger core which comprises the steps of providing a continuous length of elongated flat sheet blank having internally disposed therein at least one longitudinally extending stratum of separation defining a corresponding longitudinally extending embryonic passageway laterally contained and defined within unseparated portions of said blank, deforming said blank along spaced portions thereof into first bends transverse said embryonic passageway and alternately extending in opposite directions, reversely bending said blank at said portions into a serpentine configuration through an interleaved array of spaced parallel spacing means to form second bends of about at said portions of greater radius than said first bends whereby the inner portions of said blank opposite said separation at said second bends are bulged away from their complementary outer portions opposite said separation, and subjecting said bent tube blank along said stratum to internal fluid pressure sufficient to open a longitudinally extending tubular passageway While distending the walls of said blank intermediate a'djacent second bends into contiguity with the opposing parallel sides of said spacing means whereby said tubular passageway at second bends is formed substantially free from constriction.

9. The method of claim 8 wherein the serpentine configuration is arranged by moving two opposing arrays of 7 spaced parallel mandrels as the spacing means in opposition to each other into interdigital relationship and simultaneously bringing the mandrels into closer spacing while maintaining the length of said blank between said arrays the mandrels of which act on adjacent portions of said blank in alternate directions.

References Cited in the file of this patent UNITED STATES PATENTS f Smith Mar. 30, 1954 

